LOCATION COCHRAN CAEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic, mesic Aridic Argixerolls
TYPICAL PEDON: Cochran very cobbly loam--on a 6 percent west-facing slope under mountain big sagebrush, bluebunch wheatgrass, and Thurber's needlegrass at 5,340 feet elevation--rangeland. (Colors are for dry soil unless otherwise noted. When described on August 27, 1980 the soil was dry throughout.)
A1--0 to 5 inches; brown (10YR 5/3) very cobbly loam, very dark grayish brown (10YR 3/2) moist; moderate thick and very thick platy structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine roots, many very fine interstitial pores; 3 percent stones, 20 percent cobbles, and 30 percent gravel; neutral (pH 6.6); clear wavy boundary.
A2--5 to 11 inches; dark grayish brown (10YR 4/2) very cobbly loam, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; hard, very friable, moderately sticky and slightly plastic; many very fine, common fine and few medium roots; common very fine interstitial and tubular pores; 5 percent stones, 20 percent cobbles, and 30 percent gravel; neutral (pH 7.0); clear wavy boundary. (Combined thickness of the A horizons is 8 to 18 inches)
Bt1--11 to 19 inches; yellowish brown (10YR 5/4) extremely cobbly clay loam, dark brown (10YR 3/3) moist; strong medium and coarse angular blocky structure; very hard, friable, moderately sticky and moderately plastic; common very fine and few fine and medium roots; many very fine interstitial and common very fine tubular pores; common faint and distinct clay films on faces of peds and lining pores; 5 percent stones, 35 percent cobbles, and 30 percent gravel; neutral (pH 7.0); gradual smooth boundary.
Bt2--19 to 31 inches; light yellowish brown (10YR 6/4) very gravelly clay, brown (10YR 4/3) moist; moderate fine and medium prismatic structure parting to strong medium and coarse angular blocky; very hard, very sticky and very plastic; few very fine, fine and medium roots; common very fine interstitial and tubular pores; common faint and distinct clay films on faces of peds and lining pores; common pressure faces; 5 percent stones, 5 percent cobbles, and 40 percent gravel; neutral (pH 7.0); clear wavy boundary. (Combined thickness of the Bt horizons is 17 to 32 inches)
2BCt--31 to 48 inches; light yellowish brown (2.5Y 6/4) extremely cobbly loam, olive brown (2.5Y 4/4) moist; moderate fine and medium angular blocky structure; hard, very friable, moderately sticky and slightly plastic; few very fine, fine and medium roots; many very fine interstitial pores; few faint clay films bridging mineral grains; 10 percent stones, 20 percent cobbles, and 40 percent gravel; slightly alkaline (pH 7.5); clear wavy boundary.
2C--48 to 72 inches; light yellowish brown (10YR 6/4) stratified extremely cobbly loam, sandy loam and loamy coarse sand, dark yellowish brown (10YR 3/4) moist; massive; hard, very friable, nonsticky and slightly sticky and nonplastic and slightly plastic; pockets of common very fine and fine roots; many very fine interstitial pores; 15 percent stones, 35 percent cobbles, and 30 percent gravel; slightly alkaline (pH 7.5). (Combined thickness of the BCt and C horizons is 15 to more than 30 inches)
TYPE LOCATION: Lassen County, California; east of the Madeline Plains about 6.1 miles south of Madeline; found by going to the intersection of County Road 535 and U.S. Highway 395, then about 1,900 feet along County Road 535 to a trail, then 100 feet east of the County Road and 50 feet south of the trail; about 1,300 feet west and 100 feet north of the southeast corner of section 8, T. 36 N., R. 13 E.; USGS McDonald Peak 7.5 minute topographic quadrangle; 40 degrees 57 minutes 45 seconds north latitude and 120 degrees 29 minutes 47 seconds west longitude, NAD27.
RANGE IN CHARACTERISTICS:
Soil moisture - The soil moisture control section (10 to 25 inches) is moist in all parts from about December 1 through April 15. It is dry in all parts from June 15 through November 15 (153 days). The soil temperature exceeds 41 degrees from April 1 through December 1 and exceeds 47 degrees F from May 1 through November 15; Aridic moisture regime that borders on xeric.
Mean annual soil temperature - 47 to 50 degrees F.
Mollic epipedon thickness - 11 to 19 inches; includes the Bt1 horizon.
Depth to base of argillic horizon - 30 to 50 inches.
Particle-size control section - Clay content: Averages 35 to 50 percent; Rock fragments: Averages 50 to 60 percent, mainly cobbles and gravel. Lithology of fragments are volcanic rocks such as basalt and andesite.
Other features - Rock fragments on the surface, mostly stones and cobbles, range from 15 to 40 percent.
A horizon - Dry color: 10YR 4/2, 5/2, or 5/3.
Moist color: 10YR 2/1, 2/2, or 3/2.
Rock fragments: 40 to 75 percent; gravelly phases have 25 to 30 percent gravel.
Organic matter content: 1 or 2 percent.
Bt horizons - Dry color: 10YR 4/2, 4/4, 5/3, 5/4, 6/3, or 6/4.
Moist color: 10YR 2/2, 3/3, 3/4, 4/2, 4/3, or 4/4.
Texture: Very gravelly clay or extremely cobbly clay loam.
Clay content: 35 to 45 percent in the Bt1 horizon and 45 to 50 percent in the Bt2 horizon.
Rock fragments: 50 to 80 percent.
Organic matter content: 0.5 to 1 percent.
2BCt and 2C horizons - Dry color: 10YR 6/4; 2.5Y 6/2 or 6/4.
Moist color: 10YR 3/4 or 4/4; 2.5Y 4/2 or 4/4.
Texture: Stratified extremely cobbly loamy coarse sand to extremely gravelly loam.
Clay content: 5 to 15 percent.
Rock fragments: 70 to 85 percent.
Reaction: Neutral or slightly alkaline.
COMPETING SERIES: These are the Adelmann (T), Cassiro, Eglirim, Fivesprings, Nammoth, Pickup, and Ruclick series.
Adelmann soils have mean annual soil temperature of 52 to 54 degrees F. and have the base of the argillic horizon of more than 60 inches. Cassiro soils are deep to paralithic contacts and are moderately acid in the argillic horizon. Eglirim soils are dominated by stones. Fivesprings, Nammoth, Pickup, and Ruclick soils are moderately deep to lithic contacts.
GEOGRAPHIC SETTING: Cochran soils are on lake terraces. These soils formed in alluvium derived from volcanic rocks. Slopes are 2 to 15 percent. Elevation ranges from 5,300 to 5,500 feet. The climate is semiarid with cold, moist winters and warm, dry summers. The mean annual precipitation is 12 to 14 inches and includes 10 to 30 inches of snow. The mean July temperature is 62 to 66 degrees F., the mean January temperature is 25 to 28 degrees F., and the mean annual temperature is 44 degrees to 46 degrees F. The frost-free period is 60 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Devada, Fiddler, Lakeview, and Termo soils. Devada soils are shallow to lithic contacts. Fiddler soils are moderately deep to lithic contacts and have a xeric moisture regime. Lakeview soils are fine-loamy. Termo soils are very fine, have ochric epipedons, and natric horizons.
DRAINAGE AND PERMEABILITY: Well drained; very high surface runoff; slow permeability in the upper part over moderately rapid permeability in the lower part.
USE AND VEGETATION: Cochran soils are used for rangeland. The vegetation is mountain big sagebrush, Idaho fescue, bluebunch wheatgrass, and Thurber's needlegrass.
DISTRIBUTION AND EXTENT: Northeastern California. These soils are not extensive with about 8,000 acres of the series mapped to date. MLRA 23.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES ESTABLISHED: Lassen County (Susanville Area Soil Survey), California, 2000.
REMARKS: Diagnostic horizons or features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 19 inches (A1, A2, and Bt1 horizons).
Argillic horizon - The zone from 11 to 31 inches (Bt1 and Bt2 horizons).
Particle-size control section - The zone from 11 to 31 inches (Bt1 and Bt2 horizons).